Common Knowledge | When Should You Cite Something?

In academic writing, the concept of “common knowledge” refers to information that an average educated reader would accept without needing the validation of a source reference.

There are two main categories that can be considered common knowledge:

  • Information that most people know.
  • Information shared by a specific group of people, such as a national or cultural group, or members of a certain professional field.

In academic writing it is important to cite your sources, but statements that are considered common knowledge do not need a citation.

Common knowledge test

What is common knowledge?

Many examples of common knowledge include information that appears across many sources without a clear origin for example, famous historical dates. It also includes long-established facts or theories that are considered foundational to a field  for example, fundamental equations in physics.

Common knowledge does not include data and statistics gathered in empirical studies  you should always cite the source of such figures. It does not include interpretations or arguments. If a statement can be disputed, you should provide a citation.

The purpose of citation is to acknowledge the source of your information and ideas, to avoid plagiarism, and to allow the reader verify your claims. You do not need to cite common knowledge because it is widely known, undisputed and easily verified, and it generally cannot be attributed to a specific person or paper.

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How to identify common knowledge

If you are unsure whether or not a statement counts as common knowledge, ask yourself these questions, or refer to these examples.

  1. Who is my reader and what can I assume they know?
    Are you writing for a general audience or for experts in the field? In academic writing, it is more likely that your reader will be an expert, and you can assume a certain level of shared knowledge. But if you include information from a different field, you should cite it.
  2. Could my reader dispute this statement?
    If your reader might be surprised by your statement, question its accuracy, or contest it with other data, it is not common knowledge and you should provide a citation. If it is a foundational fact that everyone in the field agrees on, it is probably common knowledge.
  3. Can my reader easily verify this statement across multiple sources?
    If you Google it, can you easily find more than five scholarly sources that give the same information? If yes, it is probably common knowledge. If some of the search results contradict each other or you have to dig further to find the facts, you should provide a citation.

Examples of common knowledge

The examples below indicate the subtle differences in what is considered common knowledge.

Yes: APA is a common citation style used by students.
This is an undisputed and easily verified fact.

Maybe: The APA reference style is mainly used in social sciences, business and nursing.
For a reader familiar with research, this is likely to be accepted as common knowledge.

No: The APA citation style is used in more than 90,000 papers per year. 
This is not an undisputed fact, and should be attributed to one or more sources.

Yes: The Amazon is the world’s largest tropical rainforest.
This is a widely known fact that you can assume any reader will accept.

Maybe: Due to deforestation, the Amazon has been rapidly decreasing in size since the 1960s.
If you are writing an in-depth paper on the Amazon for an expert reader, this would likely be accepted as common knowledge. If you are writing a basic or introductory paper for a more general audience, you should provide a citation.

No: The cattle sector is responsible for 80% of deforestation in the Amazon.
This is a statistic derived from specific research, and should be cited even if it is widely accepted to be true. You should always give the source of figures and statistics.

Do you have to cite common knowledge?

Common knowledge does not need to be cited in your paper. However, to avoid plagiarism, you should be absolutely certain a piece of information is considered common knowledge before you omit the reference.

Remember that in an academic paper, you are unlikely to include very much information that is considered common knowledge, as the nature of research involves exploring complex concepts.

It can be tempting to cite every sentence to be safe, but in some cases over-citation can weaken your academic writing. If in doubt, you should consult your supervisor, professor or department.

Make sure you avoid all types of plagiarism by always using your own words and citing whenever you use someone else’s research, ideas or arguments. Scribbr’s plagiarism checker can help ensure your work is original.

Quotations, proverbs and idioms

You should always provide a citation when you quote someone else’s words. However, sometimes you might use phrases that are not your own, but that are not attributable to a single source  for example, proverbs and idioms.

If the phrase is widely used in your reader’s cultural and linguistic context, it counts as common knowledge. In general, though, you should avoid idioms and informal phrases in academic writing.

Frequently asked questions

Do you have to cite common knowledge?

Common knowledge technically does not need to be cited. However, you should be extra careful that this knowledge is, in fact, considered common.

Common knowledge encompasses information that the average educated reader would accept as true without needing the extra validation of a source or citation.

Common knowledge should be widely known, undisputed and easily verified. When in doubt, always cite your sources.

Do I have to include a bibliography or reference list?

In Chicago author-date style, your text must include a reference list. It appears at the end of your paper and gives full details of every source you cited.

In notes and bibliography style, you use Chicago style footnotes to cite sources; a bibliography is optional but recommended. If you don’t include one, be sure to use a full note for the first citation of each source.

How can I summarize a source without plagiarizing?

To avoid plagiarism when summarizing an article or other source, follow these two rules:

  • Write the summary entirely in your own words by paraphrasing the author’s ideas.
  • Cite the source with an in-text citation and a full reference so your reader can easily find the original text.
Can plagiarism be accidental?

Accidental plagiarism is one of the most common examples of plagiarism. Perhaps you forgot to cite a source, or paraphrased something a bit too closely. Maybe you can’t remember where you got an idea from, and aren’t totally sure if it’s original or not.

These all count as plagiarism, even though you didn’t do it on purpose. When in doubt, make sure you’re citing your sources. Also consider running your work through a plagiarism checker tool prior to submission, which work by using advanced database software to scan for matches between your text and existing texts.

How is plagiarism detected?

Plagiarism can be detected by your professor or readers if the tone, formatting, or style of your text is different in different parts of your paper, or if they’re familiar with the plagiarized source.

Many universities also use plagiarism detection software like Turnitin’s, which compares your text to a large database of other sources, flagging any similarities that come up.

It can be easier than you think to commit plagiarism by accident. Consider using a plagiarism checker prior to submitting your paper to ensure you haven’t missed any citations.

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Shona McCombes

Shona has a bachelor's and two master's degrees, so she's an expert at writing a great thesis. She has also worked as an editor and teacher, working with students at all different levels to improve their academic writing.